2.5L ('98-'01) Misfire Issues

[americanclassic16]

Hello everyone,
I've been pretty issue-free for the past two years but that suddenly changed a few days ago. Thankfully I was able to find my account and even managed to remember the password on the first try!

As for my issue, it's a 1999 2.5L with 140k on it that just ran into some serious misfire problems. A few days ago I was driving around and suddenly it just started driving really rough. I figured it was a misfire and sure enough I got a blinking CEL to go with it and had to drive home about 10 miles until I could pull the code. Now for the longest time I've been getting this intermittent P0302 that would pop up every few months then go away. I figured whatever was causing that probably just escalated to cause this much bigger issue but surprisingly, the code I pulled that day was actually on cylinder 1 (P0301).

Ever since I have owned the truck, it has always had some hesitation on acceleration that has never really gotten worse over the years but has definitely been there. I had suspected it was a minor compression issue (because that's just my luck) but as long as it ran, I didn't care. Well, I finally had to bite the bullet and did a compression test and to my extreme surprise all cylinders tested around 150 psi! I was happy to rule compression as an issue but now I've been left scratching my head without a solid lead on what to do next.

Today, I finally took it for another drive to make sure the problem persisted. For the first 15 minutes or so, it acted as it normally had but then it suddenly started misfiring really badly again. This time, I got three codes: P0300, P0301, and P0302. I really feel as if this is more of the random misfire problem because when I drive it, it really does seem as if the misfires are very well distributed among all cylinders. There's no rhythm to it, it's really quite even (at least as "even" as a misfire can be). Also, for what it's worth, the misfire seems to be worst at lower RPMs and especially right after a shift. If I really press down on the gas the misfire seems to subside a bit but I really don't know how to interpret this.

Based on my previous experiences, I think I can rule out the fuel pump (since I have dealt with that issue before and it feels nothing like that) and I did replace the spark plugs and wires a few years ago. I'd sure like to hear what you folks have to say about it. Thank you!

-Americanclassic16

 

[RonD]

Welcome back, sorry for the trouble though

The 1995 to 2001 2.3l and 2.5l Limas have a unique feature you can use for a test
After engine is warmed up, shut it off
Unplug the 3 wire connector on one coil pack
Restart engine
Listen for misfires raise RPMs see if you get CEL
The Limas ran fine on 4 spark plugs from 1974 to 1988 so will still run fine unless there's a problem with those 4 spark plugs

Shut off engine, read and clear the codes and do same test but using the other coil pack
Codes will indicate steady misfire with only 4 spark plugs being used

What can happens that 1 spark plug in a cylinder can fail(p0302?), but you will never know it until other spark plug in that same cylinder starts to have an issue
The benefit and curse of dual spark plugs

 

[americanclassic16]

So I got it warmed up to where it started misfiring again and I did the test you suggested. Here are the results:
After I warmed it up and shut it off (before disconnecting anything), I pulled the code (P0301) and then cleared it.

I disconnected the exhaust side coil pack first and noticed it ran similarly to before. The misfire seemingly disappeared at higher RPMs (the truck stopped shaking at least) and was probably worst right when I let off the gas and the RPMs were the lowest. I didn't get any check engine lights for the minute or two that I was doing the test but I did pull and clear two pending codes (P0301 and P0302) after I shut it off.

Then, I reconnected the exhaust side and disconnected the intake side and it ran much worse. Like the first time, the misfire disappeared at higher RPMs but was really bad to the point of almost stalling as soon as I let off the gas and let it idle. This time though, I didn't get any codes but I can certainly say that it ran much worse and hesitated a lot on acceleration with just the exhaust coil pack connected. Also, for both cases, I noticed a rhythm this time and it seemed like it could very well be the spark plugs in cylinders 1 and/or 2 misfiring.

So just to make sure I understand, this test was to see if the spark was the problem, correct? If both sides had performed identically, then it would've ruled out all the things that were changed between the two tests (spark plugs) and indicated something that didn't (injectors, vacuum leak, etc). Since changing which spark plugs fired changed how the engine ran, then it seemingly indicates the spark plugs are at fault for the misfire. That's a pretty ingenious test! If my reasoning is off, please correct me but for now, I'm going to rest a bit easier thinking it could be something as easy as the spark plugs/coil pack at fault!

 

[RonD]

Good testing

Your reasoning is spot on

At least some(or all) of the issue is spark related, for sure

But looking at the spark plug tips may tell another tale, just have to look and see

Spark plugs are a pain to change on this engine, but I think that's were I would start, at least on the exhaust side
And I would be tempted to buy 1 coil pack, just to swap in and repeat the testing

You can test spark plug wires pretty easily, rule of thumb is 5,000 ohms per foot
Set OHM Meter for 200k, if there is a selection
24" wire would show 10.000, which is 10k, 8k to 12k would still be fine
18" wire would be 7.500, 7.5k, 6k to 9.5k would be fine
ect..........

If a wire is cracked or melted replace it regardless of test

 

[americanclassic16]

I did forget to mention that when I was doing the compression test the four spark plugs I looked at looked normal (though I'm still happy to replace them as it's certainly the cheapest fix). I agree that it's a pain to replace them but I remember when I was replacing the lower intake manifold gaskets a while back that if I had removed the air hose and the throttle body it would've made the intake side a lot more accessible without too much work. I'll have to give that a shot this time around.

Also, as a random side note, if you're ever buying parts from a local chain store, you can almost always get 25% off if you just buy online from advance auto (even if you're just going to pick them up in store 30 minutes later). Just look up coupon codes for Advance Auto and there's usually at least a 20% one going around. Same price as Autozone or O'Reilly's usually but -25%. I just remembered thought about that when I was looking for motorcraft plugs this afternoon, 8 plugs at 4.99 a piece = $40 but using that coupon code from Advance, it's only $30. That might come in handy sometime, always nice to save money!

 

[golley]

retailmenot.com lists many discount deals at several parts store chains.

 

[americanclassic16]

Hey folks, I've been busy for a while but I finally got around to trying the suggested fixes on my truck. Short story: didn't work, but there's a lot more to it then that. The first fix was to replace the plugs and wires which I did and it didn't make much difference. When I was taking out the plugs, the tips all looked pretty good (normal wear) but I noticed the plugs were gapped a bit smaller than they should have been (which I must've done the last time I put them in). After driving around for a bit, I noticed that the misfiring happened a lot sooner than usual. Since the plugs had a larger gap now and the coil had to do more work, I thought it was possible the coils were at fault. I found a set on Amazon that looked good (and only $30 for the set) so I finally got them today and swapped them in. At first, it seemed a lot better but soon enough, the misfiring started again. When I got home and got out of the truck, I noticed the unburnt gas smell that normally accompanies my truck was completely gone. I idled it for a bit longer and confirmed that the gas smell was gone. I thought a bit longer about it and figured that the exhaust side coil (which throws the exhaust spark to burn the remaining gas) could've been bad (which caused the result from the coil pack test I did) so I went back out while the truck was still warm and did the test again. As it turned out, there was no difference between the two coil packs operating alone now and still no unburnt gas smell so even though it didn't fix the problem, I'm fairly sure the exhaust side coil pack wasn't working properly. What should I do now?

 

[RonD]

First, dual spark plugs in any engine were never used to "burn remaining gas", take that OUT of your knowledge base, it is incorrect
Dual spark plugs make more power, BOTH fire at the same time, no alternating, another Myth on the 2.3l setup

Ford uses a Waste spark system, first spark system ever used back in the 1880's, and still used today
Spark is timed by the Crank shaft, so spark is used at each TDC of each cylinder, so on a 4-stroke engine that means 1 spark on compression stroke and 1 spark on exhaust stroke, so 1 spark is "wasted", hence the name
Both spark plugs in each cylinder always fire at the same time, compression and exhaust stroke
There is no way a spark plug could ignite any "remaining fuel" unless it was compressed, like on the compression stroke
The exhaust spark is done because without a distributor is just a simpler and better way to time spark

Why don't all engines use dual spark plugs?
It was hard to do that with distributors, although there were quite a few that did try it
With advent of distributorless system several engine used dual plug, i.e. Dodge Hemi, but hard to find the head space to make it practical
Then 4 valves in each cylinder(DOHC) came along and makes even more power than dual spark plugs, so a better use of head space in a cylinder
The 2.3l/2.5l Lima engine was designed in the early 1970's and then first used in a 1974 Pinto, so fuel injection and dual spark plugs were add-ons that could be used with the older design until the 4-valve 2.3l Duratec was made available in late 2001 Rangers

So you have run the engine on just 4 spark plugs, unplugging 1 coil pack, and it runs OK on either coil pack?
So all 4 spark plugs on each coil pack are working
What Gap did you end up using?

Then you are left with compression and fuel as the culprit

 

[americanclassic16]

Thanks for the info about the dual spark system, I've heard so many things about it over the years but that finally makes sense! I guess I should've been a bit clearer with how it ran with the new coil packs. It still misfires after it gets warmed up, it just runs equally as poor whether the intake or exhaust side coil pack is disconnected. There isn't a difference unlike there was before when I did the test prior to replacing the coil packs. I gapped the plugs at 0.045, the ones I took out were around 0.040. All the plugs/wires/coils should be working and I've already done a compression test which seemed to check out. I've dealt with fuel issues before on this truck and replaced the filter and pump two years back. I'm starting to run out of straightforward things to investigate, I suppose fuel pressure and injectors would be next on the list. What do you suggest?

 

[RonD]

Yes, if you can test fuel pressure, expected on 1998 and up Rangers is 55-65psi(1997 and earlier was 30-40psi) engine running, then increase RPM to about 2,000 and hold it there for 30 seconds and watch if pressure is dropping, it shouldn't
If increase in RPMs(fuel demand) causes loss of power then fuel pressure would fit

The 2.3l/2.5l Lima engines ran fine from 1974 to 1988(14 years) on 4 spark plugs and a distributor
So will run fine with either coil pack unplugged, just LESS POWER than with dual spark plugs, that should be the only difference
There should be no misfiring on just 1 coil pack compared to 2 coil packs

 

[americanclassic16]

An interesting development with regards to my truck: when I initially made the coil pack fix, I took it for a drive and still got a misfire as explained in the previous post. It would not, however, set any codes as it had previously (P0301, P0302, P0300). Well, I wanted to look a bit more into the fuel pressure angle and see if it had lost power going up hills (which I had noticed on the last drive a bit) and took it for a longer drive today. It did seem like that was the case as I was driving it today but I was intent on making it set a code this time so I made sure to run it in the low RPM range where it ran the roughest. I didn't get any CEL on the dash when I concluded my drive but I still figured i'd check for pending codes. Results: a P0136! An O2 sensor code? I've never dealt with this before and am still looking into how that fits into the picture but I thought i'd let the experts here on the forum in on this development. What do you think? Could this be the whole problem? I will have my OBDII bluetooth tool back in a few days so I can actually check the voltage on the O2 sensor but until then, does this seem like it could be the culprit?

 

[RonD]

P0136 02 Sensor Circuit Malfunction (Bank 1 Sensor 2)

This is a Sensor 2 issue, sensor 2 is the O2 behind the Cat converter, its there to test if Cat is cleaning up the exhaust, i.e. burning up toxic emissions, while this can be a telltale issue that engine is not running correctly it can not cause the engine to run incorrectly

Its like the fuel gauge being on empty and the engine stalling, the gauge didn't cause the engine to stall, running out of gas did

Sensor 2 should run at .7-.8volts, low oxygen, should be fairly steady, but will jump now and then as computer sends extra fuel to keep the Cat(s) hot

And the Code indicates a "circuit" malfunction, so check the wires and connector for this O2, computer didn't use low or high voltage code, so more like a "no connection code", wiring issue

The Bank 1 sensor 1 is the O2 the computer uses to adjust air/fuel mixture, its voltage will jump around alot
Sensor 1s failing will cause running issues
A V6 or V8 will have two sensor 1s

In any case the P0136 code is not a clue to your running issues

 

[americanclassic16]

I read about O2 sensors some more right after I made that post and saw that it was indeed more of a symptom than a cause. I went driving again today to get some O2 sensor data that seemed to indicate it could be bad (read 0.0v at one point) but the throttle position sensor raised a few questions as well. I know that it's technically a potentiometer so you wouldn't necessarily expect 0 at idle and 100 at WOT but based on some reading I did, the symptoms I've seen are very similar to what a bad TPS would cause. The TPS sensor on my truck read 12% at idle and maxed out at 60% WOT. How far off would you expect these readings to be or is it really just dependent on the vehicle? A new TPS is only $20 on Amazon so if fuel pressure checks out, I may just give that a shot. It'd explain the rough idle and the really bad hesitation. What do you think?

 

[RonD]

TPS uses a 5 volt scale
At throttle closed it should be at .69-.99 volt, under 1 volt, so under 20%, so 12% is OK, but 16-17% is expected
At WOT it should be 4.5-4.8volts so over 89%, so 60% is low

Check if your throttle cable has stretched, use a stick on gas pedal to hold it down
Then open the hood and see if you can manually open the throttle more, if so do the "throttle cable mod", its very easy to do

 

[americanclassic16]

Well, it looks like iv'e killed another fuel pump. I also checked the throttle cable and it definitely is stretched, it continued a good ways after I put the pedal to the floor. I haven't done an official fuel pressure test but I depressed the pin in the schrader valve to see if there was any pressure and the fuel barely trickled out. Definitely not 55-65 psi, even after I put the key in accessory power.